1. Field of the Invention
This invention relates to a condensation heat transfer facility having therein a primary body of hot saturated vapor with a secondary body of vapor interposed between the primary body of vapor and the atmosphere. In particular, the invention is directed to a method for maintaining the secondary body of vapor.
2. Description of the Prior Art
Various diverse operations such as soldering, fusing, brazing, curing, cooking, etc. require that articles be heated to elevated temperatures. One method of heating articles to the desired elevated temperatures is described in U.S. Pat. No. 3,904,102 to Chu et al. which issued on Sept. 9, 1975 and is assigned to the assignee of the instant invention.
The Chu et al. patent describes a condensation heating facility which is open to the atmosphere in order to facilitate the entry and removal of articles therefrom. The articles to be heated to elevated temperatures are placed in a primary body of hot saturated vapors where a portion of the vapor will condense thereon and transfer thereto its latent heat of vaporization to heat said articles. A secondary body of vapor of a relatively inexpensive material is interposed between the relatively expensive primary body of saturated vapor and the atmosphere to reduce or substantially eliminate losses to the atmosphere of the hot primary vapor due to convection, diffusion and drag-out.
Although the secondary body of vapor has been found to be effective to reduce significantly the losses of the expensive primary vapor, a portion of both the primary and secondary vapors are continuously lost to the atmosphere across the secondary vapor-air interface. A significant contributor to such losses has been found to be the method of providing supplemental secondary vapor in order to maintain the secondary body of vapor. A most important parameter relating to the above-referred to losses is the disturbance to the primary-secondary vapor interface when generating supplemental secondary vapor. Such a disturbance will increase the loss of the secondary vapors and, more importantly will result in additional losses of the expensive primary vapors to the atmosphere.
The secondary body of vapor may be supplemented by (a) vaporizing a secondary liquid by feeding said liquid directly into the hot primary liquid, (b) vaporizing the secondary liquid by spraying it over the hot primary-secondary vapor interface, or (c) providing a secondary vapor generator, outside the facility, which communicates with and supplements the body of secondary vapor.
Although all of the above methods have each met with a measure of success in maintaining the secondary body of vapor, each has definite drawbacks. The feeding of a secondary liquid directly into the hot primary liquid or spraying of such liquid over the primary-secondary vapor interface causes violent mixing resulting in additional losses of the expensive primary vapor to the atmosphere. The use of a secondary vapor generator necessitates additional expensive apparatus which requires a high degree of control.